Visualization of Rise in Temperature Induced by High Intensity Focused Ultrasound in Tissue
High intensity focused ultrasound (HIFU) creates a focused sound field with the highest pressures in a 2mm x 10mm cigar shaped region (with our transducer). Significant heating (over 30 degrees Celsius) occurs primarily within the concentrated region where the sound pressures are highest. This means surrounding tissue can be spared from injury. However the exact heating patterns are not known. For example the HIFU can form bubbles with heating and increase the attenuation by more than a factor of 2 preferentially. The goal of this study is to make a map of the temperature field in the tissue created by HIFU and to simultaneously measure the acoustic attenuation. Our transducer was bowl-shaped, running at 2 MHz, with a single element. We used an acoustic power of 27 and 54 watts. For our experiment the transducer was mounted on a box. The temperature measurements were made with an infrared camera. Since the camera could only take pictures at surfaces, we stacked two slabs of liver in a box, such that their interface was along the axis of the transducer. The attenuation data ranged from the x-y, which fit well with the range in the literature and with the lowest value being for degassed liver. The thermo camera and attenuation data will be used to calibrate a numerical code designed to predict the temperature field in the liver. Our combined results will then be used to predict effective treatment dosages and guide HIFU treatments.
